RE-DATING PALLETT CREEK PALEOEARTHQUAKES WITH AMS CARBON-14 TECHNIQUES

Pallett Creek, CA is located ~55 km northeast of Los Angeles on the San Andreas fault. Originally excavated and studied by Kerry Sieh between the late 1970's and 1980's, paleoearthquake evidence from the site provides important constraints on fault behavior and has shaped subsequent paleoearthquake studies. We are re-dating the paleoearthquakes documented by Sieh using AMS carbon-14 (C14) methods and will compare these dates with (1) the original dates determined by conventional C14 techniques and (2) nearby paleoearthquake sites dated with AMS C14 such as the Wrightwood site. We resampled the upper section of the site, collecting oriented brick-sized samples for later examination in the lab. Under the microscope, the organic-rich layers contain a significant amount of detrital charcoal and charcoal dust, sparse seeds and other macrofossils, and less peat (i.e., decomposed organic material) than expected. Approximately 50 new C14 dates are pending and will be presented. The abundance of charcoal observed suggests that a different approach to refining the layer ages may be appropriate, wherein the youngest detrital date for each layer is used as the layer age, rather than calculating the layer age by combining individual dates from each layer into a single layer age. We will compare these approaches and evaluate the impact of each layer age model on the paleoearthquake ages.